Oil and gas hydrocarbons occur in some subterranean formations. In the petroleum industry, a subterranean formation containing oil, gas, or water is referred to as a reservoir. In order to produce oil or gas, a well is drilled into a reservoir or adjacent to a reservoir. A well can include, without limitation, an oil, gas, or water production well, an injection well, or a geothermal well. A well may include at least one wellbore. The wellbore is drilled into a subterranean formation. The wellbore may be an open hole or cased hole. In an open-hole wellbore, a tubing string may be placed into the wellbore. In a cased-hole wellbore, a casing is placed into the wellbore that can also contain a tubing string. Drilling fluids may be introduced into or flowed into the wellbore through the tubing string.
In drilling oil wells, a mud-like drilling fluid is pumped into the wellbore to clean and cool the drill bit and to flush to the surface the rock cuttings that are torn loose by the drill bit. The drilling fluid must have certain physical characteristics. The most important of these is the viscosity and the water holding or retaining characteristics of the fluid. Drilling fluids lubricate and flush rotary drill bit cuttings from the wellbore. They also provide hydrostatic pressure or head in the wellbore to control pressures that may be encountered in the subterranean formations. The density or weight of the drilling fluid creates a hydrostatic pressure against the pipe that is greater than that in a porous subterranean formation traversed by the wellbore. In water-based drilling fluids, this is due to the filtrate, or water in the drilling fluid, that flows through the wellbore wall into the low pressure earth formation.
However, filtrate loss is a long-standing problem in the petroleum industry. Filtrate loss can be described as the amount of drilling fluid filtrate lost into the subterranean earth formation because of the pressure differential between the formation pressure and hydrostatic pressure of the liquid in the wellbore. A sub-optimal fluid loss control may result in creation of a bridge in a wellbore annulus opposite a permeable zone. This may result in the isolation of a lower zone from the hydrostatic pressure above the bridge. It has been observed that only a small amount of filtrate loss beneath such a bridge cause a drop in the annular pressure to below that of the formation pressure. As a result, there is an influx of formation fluids and pressure. This may create flow channels and require expensive remedial work. The lost fluid may also damage sensitive formations. It is, therefore, important to control fluid loss from wellbore servicing fluids to the surrounding formation.